1. Field of the Invention
This invention relates to improved thick film sensors for detection of magnetic bubble domains, and more particularly to a sensor configuration which provides soft error detection and full data rates.
2. DESCRIPTION OF THE PRIOR ART
Various techniques for sensing magnetic bubble domains are known in the art. Some of these utilize magnetoresistive elements which are of the same thickness as the magnetic elements used to propagate the bubble domains in a host magnetic medium. For instance, a chevron propagation circuit and chevron sensor having the same thickness are shown in U.S. Pat. No. 3,713,120. Additionally, IEEE Transactions on Magnetics, Volume MAG-9, No. 3, pp. 474-480, September 1973 describes a fabrication technique for making magnetic bubble circuits using single masking level processing. In this type of processing, the magnetoresistive sensor is deposited at the same time as the magnetic propagation elements, and has the same thickness as the propagation elements. Of course, this is advantageous from a processing standpoint and overcomes some of the problems, such as corrosion, etc., which are associated with thin film detectors having thicknesses of the order of approximately 200-400 Angstroms.
In spite of the advantages of the thick film chevron detectors, there are disadvantages with such detectors as was pointed out by R. A. Baugh, R. B. Clover, and L. S. Cutler ("Some Aspects of Magnetic Bubble Memory Module Design"), which was presented as invited paper 22.2 at the 1974 International Conference on Magnetics (Toronto, May 1974). As those authors point out, thick film chevron expander-detectors are not routinely used to sense bubble domains at a data rate equal to the data rate of the bubble domain in the propagation circuits. This is a limitation of the sensor itself wherein the thick film chevron sensor often has two bubble domains in magnetic field coupling promixity to it during certain phases of a single cycle of the rotating magnetic drive field. Therefore, the sensor provides a sense signal which is a combination of signals due to two data bubble domains. In order to compensate for this, it has been customary in the past to detect with the sensor only in every other cycle of field rotation.
In the practice of the present invention, a configuration is shown which enables the use of thick film magnetoresistive elements for bubble domain sensing at a rate equal to the rotating magnetic drive field frequency, thereby overcoming the aforementioned disadvantage of the prior art. Additionally, the present invention can also be configured to provide soft error detection, where "soft errors" are any errors associated with the bubble domain sensor. As an example, such errors are those produced by faulty sensors or by sensors having improperly working sense amplifiers associated therewith. Another type of soft error is that due to the metallurgy or fabrication of the sensor element itself. Generally, these soft errors include any type of error which can be attributed to the sensor or the circuitry associated with the actual sensing element.
In the practice of the present invention, sensor-dummy pairs are used for detection of the bubble domains, where the dummy sensors actually respond to the same bubble domain to which the associated sensor responds. In this manner, the present invention differs from well known differential sensing schemes using sensor-dummy pairs, where the bubble domains never come into flux coupling proximity to the dummy sensors. Such differential sensing schemes using sensor-dummy pairs to compensate for noise, temperature variations, effect of rotating magnetic field, etc. are described in, for example, U.S. Pat. Nos. 3,883,858, 3,736,419, and IBM Technical Disclosure Bulletin Volume 16, No. 7, December 1973, p. 2395. In addition to these differential sensing schemes, U.S. Pat. No. 3,720,928 describes a sensing configuration comprised of spatially staggered sensors which respond to magnetic bubble domains in different channels at different times, thereby allowing time division multiplexing and sharing of a single sense amplifier.
As will be appreciated by those skilled in this art, thick film magnetic bubble domain sensors have not been provided which will accurately provide sensing at data rates corresponding to bubble domain propagation rates in other circuits of the magnetic chip, and which will allow soft error detection.
Accordingly, it is a primary object of the present invention to provide improved thick magnetic bubble domain sensors which can be operated at frequencies equal to that used to propagate bubble domains in the magnetic medium.
It is another object of this invention to provide a thick magnetic film bubble domain detector in which soft error detection is achieved while sensing at high data rates.
It is another object of this invention to provide an improved magnetic thick film bubble domain detector which can be fabricated at the same time and in the same deposition step as that used to fabricate propagation elements for moving magnetic bubble domains.